1. Field of the Invention
The present invention relates to a substrate processing apparatus for rotating a substrate to process the surface thereof, and more particularly relates to apparatus for processing a substantially circular substrate such as a semiconductor wafer with a cut such as an orientation flat or a notch formed therein, or processing a complete circular substrate such as an optical disk substrate mounted on a rotary table. The surface of the substrate is processed by applying processing solutions such as detergent and etchant to the surface thereof. The present invention further relates to a substrate holding apparatus for holding and rotating a substrate in such a substrate processing apparatus.
2. Description of Related Art
A spin coater, a spin drier, a spin developer used in the processing steps of a semiconductor wafer are known as substrate processing apparatus. Apparatus of this type includes a substrate holding apparatus for holding and rotating a wafer. A predetermined process is carried out on the surface of the wafer by providing a resist solution, a developer and the like on a rotating wafer, or by dropping a resist solution or a developer on a stationary wafer and then rotating the wafer.
It is well known that during wafer processing the generation of a contaminant or a defect on the surface of a semiconductor wafer must be suppressed. Consider a case where a wafer skids on a substrate holding apparatus during rotation of the wafer in a rotary substrate processing apparatus. This may result in the bottom of the wafer being abraded against the wafer holding apparatus to generate particles, or the flow of the processing solution on the surface of the wafer may be disturbed. There is also a possibility of damaging the bottom of the wafer. It is necessary to prevent the wafer from skidding in order to avoid such problems.
A conventional substrate holding apparatus known to prevent such skidding of a wafer is shown in FIGS. 1 and 2. The substrate holding apparatus of FIGS. 1 and 2 is described in the document of Japanese Patent Application No. 61-285752 filed on Nov. 29, 1986 in Japan by the same assignee of the present application, claiming priority based on Japanese Patent Application No. 61-190246 filed on Aug. 13, 1986 in Japan. The Japanese Application 61-285752 was laid-open to the public as Japanese Patent Laying-Open No. 63-153839 on Jun. 27, 1988 and published as Japanese Patent Publication No. 3-9607 on Feb. 8, 1991.
Referring to FIGS. 1 and 2, the conventional substrate holding apparatus 30 includes a rotary plate 36 secured to the upper end of vertical shaft so as to be rotatable in a horizontal plane about the center axis of a vertically mounted shaft 34 having the center bottom fixed to the that extends upward from a motor (not shown). The rotary plate 36 includes six arms 52 projecting radially at equal intervals.
Every other arm of the six arms, i.e. three arms 52 have a fixed claw 38 on the surface of its respective tips for supporting the bottom of a wafer 32 and for regulating the travel of the wafer 32 in the horizontal direction. The remaining every other three arms 52 have a movable claw 40 on the surface of its respective tips for supporting the bottom of the wafer 32, and pivotable between a position of urging against the periphery of the wafer 32 and a position not urging the periphery of the wafer 32. The claws 38 and 40 are arranged around the center of rotation in a circular manner.
The movable claw 40 is provided on a swingable arm 50 provided on the tip of arm 52 and pivots with swingable arm 50. Movable claw 40 includes a wafer supporting portion 42 for supporting the lower surface of the wafer, with its own axis coaxial with the center axis of rotation of swingable arm 50, and a claw portion 44 projecting from the top of the wafer supporting portion 42 and displace from the center axis of wafer supporting portion 42. When the tip of the inner surface of the claw portion 44 is directed towards the center of the rotary plate 36, wafer 32 is urged towards the center by the claw portion 44. The wafer 32 is released from the urged position by the movable claw 40 pivoting so that the tip of the inner surface of the claw portion 44 is directed sideward.
The mechanism of driving the movable claw 40 includes a link rotatable plate 48 provided at the center of the upper face of the rotary plate 36, a link 46 having one end attached swingably to the link rotatable plate 48, a swingable arm 50 having one end attached rotatably to the other end of the link 46 and the other end swingable attached to the base of the claw portion 40, a biasing mechanism not shown for biasing the link rotatable plate 48 counterclockwise, and a driving mechanism not shown for rotating clockwise the link rotatable plate 48 through a predetermined angle against the biasing force of the biasing mechanism.
Referring to FIGS. 1 and 2, the conventional substrate holding apparatus operates as follows. The link rotatable plate 48 is rotated clockwise through a predetermined angle using the driving mechanism not shown. Each movable claw 40 pivots by a predetermined angle counterclockwise about the center axis thereof, as shown in solid lines in FIG. 1, by means of the link 46 and the swingable arm 50. This causes the claw portion 44 to be displaced counterclockwise from the center and take a position not pressing the edge of wafer 32. With the movable claw 40 at this position, the wafer 32 is mounted on the wafer supporting portion of the fixed claw 38 and the movable claw 40. Then, the driving mechanism of the link rotatable plate 48 is stopped. The link rotatable plate 48 is rotated through a predetermined angle counterclockwise by the biasing mechanism not shown. The movable claw 40 pivots through a predetermined angle clockwise, as shown in chain lines with two dots in FIG. 1, by means of the link 46 and the swingable arm 50. This causes the claw portion 44 of the movable claw 40 to move toward the center of the rotary plate 36. The side face of the wafer 32 is pressed by the claw portion 44. The wafer 32 is fixed in the substrate holding apparatus 30 by means of the three claw portions 44 of the movable claws 40 pressing against the side face of wafer 32. Wafer 32 can be fixed in the substrate holding apparatus 30 even if the wafer 32 has a circular configuration.
The substrate holding apparatus 30 of FIGS. 1 and 2 requires a mechanism for driving the movable claw 40 to hold the wafer 32. This mechanism includes the link mechanism and the mechanism for driving this link in the substrate holding apparatus 30 shown in FIGS. 1 and 2. Such a mechanism for driving the movable claw 40 is complicated.
A substrate holding apparatus similar to apparatus 30 is also described in the document laid open on Jun. 10, 1987 as Japanese Patent Laying-Open No. 62-128142 and published on Jan. 8, 1981 as Japanese Patent Publication No. 3-785. This apparatus includes similarly a movable wafer clutch portion for clutching the circumference of the wafer. Therefore, the apparatus described in Japanese Patent Publication No. 3-785 has problems similar to those of the apparatus shown in FIGS. 1 and 2.
FIGS. 3 and 4 show a conventional substrate holding apparatus 60 for holding a wafer 62 without using a movable portion. Referring to FIGS. 3 and 4, the substrate holding apparatus 60 includes a rotary plate 66 having the bottom center portion fixed to the end of a shaft 64 of a motor not shown and rotatable in a horizontal plane about the center axis of the shaft 64. A wafer holding member 76 for holding the bottom of the wafer 62 at the location of an orientation flat 82 of the wafer 62, and four wafer holding members 70 are secured to the upper face of the rotary plate 66. The wafer holding members 70 are arranged on a circle on the upper surface of rotary plate 66 with the center of the circle coinciding with the central axis Z of shaft 64. The wafer holding member 76 is slightly displaced inward toward the central axis, Z about which the other wafer holding members 70 are arranged circularly. When wafer 62 is placed on substrate holding apparatus 60, the arc 68 out of the contour line of wafer 62 except for the portion of orientation flat 82 is hold by wafer holding members 70. The portion of orientation flat 82 is held by wafer holding member 76. At this time, the arc 68 of wafer 62 is coaxial with the central axis Z of shaft 64.
The wafer holding member 70 includes a wafer supporting portion 72 fixed on the rotary plate 66 for supporting the bottom of the wafer 62, and a travel regulating portion 74 provided at the center of the wafer supporting portion 72 for regulating the horizontal travel of the wafer 62 supported by the wafer supporting portion 72.
The holding member 76 provided to abut on the orientation flat 82 of the wafer 62 includes a wafer holding portion 78 fixed on the rotary plate 66 for supporting the bottom of the orientation flat 82 at the central portion thereof, and a skid regulating portion 80 projecting from the center of the wafer supporting portion 78 for regulating the horizontal travel and the rotation in the circumferential direction of the wafer 62 to prevent the wafer 62 from skidding with respect to the substrate holding apparatus 60. The wafer holding member 76 is displaced towards the inside of the arc 68 in contract to the other wafer holding members 70 being in contact with arc 68 from outside.
The conventional substrate holding apparatus 60 of FIGS. 3 and 4 operates as follows. The wafer 62 is positioned so that the orientation flat 82 is located above the wafer holding member 76. The positioned wafer 62 is mounted upon the wafer supporting portion 72 of the wafer supporting member 70 and upon the wafer supporting portion 78 of the wafer supporting member 76. Thus, the wafer 62 is supported horizontally with a predetermined distance from the upper face of the rotary plate 66. As described above, the horizontal travel of the wafer 62 is regulated by the travel regulating portion 74 and the skid regulating portion 80. While plate 66 is being rotated by a motor (not shown), skid regulating portion 80 of the wafer holding member 76 prevents the wafer 62 from skidding and rotating relative to the rotary plate 66 while the orientation flat 82 is pressed against the portion 80.
It is understood from the above description that the orientation flat 82 of the wafer 62 must be positioned appropriately with respect to the wafer holding member 76 having the skid regulating portion 80 in the conventional substrate holding apparatus 60 of FIGS. 3 and 4. It is therefore necessary to provide a mechanism for aligning the wafer 62 with respect to the rotary plate 66 in the apparatus (not shown) for providing the wafer and in the substrate holding apparatus 60. Such an aligning mechanism is not preferable because it will complicate the mechanism.
The substrate holding apparatus 60 of FIGS. 3 and 4 had another problem which will be described hereinafter. Wafers having a notch which is cut in a V-shape and smaller than the orientation flat 82 instead of the orientation flat 82 are beginning to be used. A notch has a smaller cut towards the center of the wafer in comparison with an orientation flat 82. Though the skid regulating portion is positioned at a location corresponding to the location of the notch, the displacement of the skid regulating portion towards the center of the wafer becomes smaller in comparison with the case of a wafer with an orientation flat. It is therefore difficult to prevent the skid of the wafer with such a skid regulating portion. Furthermore, in the case of a substrate for an optical disk which is a complete circle without any cut-out portions like an orientation flat or a V-shape notch. The skid regulating portion cannot be displaced with respect to the complete circular substrate. In principle, the apparatus of FIGS. 3 and 4 cannot prevent the substrate from skidding. Although the apparatus of FIGS. 3 and 4 have a simple structure, it can only hold substrates that have a relatively large cut-out portion such as a semiconductor wafer with an orientation flat.